Jake Gyllenhaal's been making an increasingly big name for himself in uncompromising, gritty screen fare - often happy to play against his boy-next-door good looks. His latest 'End of Watch' is police drama, already receiving plaudits from real cops as an accurate depiction of life on the thin blue line.

Director David Ayer has walked this ground before, with Denzel Washington's 'Training Day'. Is this his love letter to the policing profession, and how did he prepare Jake Gyllenhaal and his co-star Michael Pena for their gruelling roles? Read on...

Jake Gyllenhaal and Michael Pena in 'End of Watch'

Can you tell me a bit about the two officers at the heart of 'End Of Watch'?I wanted to show normal guys. This movie is a study in friendship and it's a study of Jake and Mike, who deliver these fantastic performances, and it's just an analysis of these normal guys who are best friends who happen to be officers dealing and processing and understanding and growing and getting married and becoming parents. I think it's a success. The cops that have seen the movie, they all say the same thing no matter what department they work with: "Finally, somebody got it right."

That must be extremely gratifying to hear.It's remarkable.

Did you encounter the opposite reaction with your scripts for 'Training Day' and 'Dark Blue', which are about the bad apples in the police force?They're more impolitic. The strange thing about 'Training Day' is that since I wrote it, I've met so many cops who say, "I know that guy. I've worked with that guy." But I'm such a technical perfectionist. I want to get all the details right - the vehicles, the uniforms, the look, the attitude, the tactics, the behaviour, the physicality - so that when cops see the movie and they tell me I nailed it, it's really rewarding to me. But for me the headline here is these unbelievable performances that Jake and Mike deliver. This movie lives and dies on their friendship and you believe that these guys have been riding in the same car for years. They make it look so easy and you feel like they're just ad-libbing the whole time but they're not, they're just running the script. It's a real testament to their ability that they could pull something like that off.

Director David Ayer - put his actors through their paces

They've both said that it wasn't the easiest journey getting to that stage. Would you agree?Yes. We rehearsed for five months before the shoot. They're both incredibly gifted professional actors and they initially started tackling the problem as professional actors. I was like, "Guys, this isn't something you're going to create with technique - it's got to be real. You've got to have that familiarity." And somewhere during this journey, somewhere during the ride-alongs and being with the real cops at 3am and running into gang members and dealing with the aftermath of shootings and firing live ammunition past each other's heads and tactical exercises and real training with the LAPD, somewhere in all of that this spark of friendship burst into flame. They're still friends to this day. When that happened, they wouldn't shut up and they drove me crazy [laughs] but it was ultimately good for the movie.

What was it like when you finally entered production?They were so locked-on by that point. They were the easiest part of filming because, as a director, once we got to that point most of my issues simply became logistical and technical. Because of their technical and tactical training, I didn't have to spend time explaining what they were doing because they knew the job. I could just say, "Ok guys, you need to do a vehicle stop on this dude." "Great, we got it", and they knew everything they needed to do because they'd been trained. "Ok guys, in this scene you gotta go in and clear this house." "Ok cool." They'd just kind of shrug and amble up and do it when I called action, and it looks fantastic because they're doing it for real. That made my life easier. They were joyous to work with. I really miss them.

You also entrusted Jake with capturing first-person footage with a video camera, which you've incorporated into the film.He shot a lot of the movie. It's insane. And it's interesting because I would tell him, "You've got this camera in your hands - it's not Jake Gyllenhaal operating the camera, it's your character operating the camera so you have to see the world through that character's eyes and figure out what about that is going to capture your attention so that you're going to want to record that on video." It added this amazing layer where not only was he my actor but he became a visual collaborator.

End Of Watch is very much a love letter to the policing profession and the difficult job its members do. Was that your intention?
It's interesting because when us Americans see our servicemen or servicewomen in uniform in the airport, we'll go up and shake their hands and say, "Thank you for your service". Because they're going into harm's way on our behalf, right? Police do this every day and no one ever walks up and shakes their hand and thanks them for their service. I have a lot of friends in law enforcement and I've heard their stories over the years and I realise that, even though the police genre is the most beaten dead horse in the film and television world, the public at the end of the day really knows very little about what they actually do. And that's what I wanted to show.

End of Watch is released on 23 November 2012. Watch the trailer below...